Dickson K S, Bilger A, Ballantyne S, Wickens M P
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
Mol Cell Biol. 1999 Aug;19(8):5707-17. doi: 10.1128/MCB.19.8.5707.
During early development, specific mRNAs receive poly(A) in the cytoplasm. This cytoplasmic polyadenylation reaction correlates with, and in some cases causes, translational stimulation. Previously, it was suggested that a factor similar to the multisubunit nuclear cleavage and polyadenylation specificity factor (CPSF) played a role in cytoplasmic polyadenylation. A cDNA encoding a cytoplasmic form of the 100-kDa subunit of Xenopus laevis CPSF has now been isolated. The protein product is 91% identical at the amino acid sequence level to nuclear CPSF isolated from Bos taurus thymus. This report provides three lines of evidence that implicate the X. laevis homologue of the 100-kDa subunit of CPSF in the cytoplasmic polyadenylation reaction. First, the protein is predominantly localized to the cytoplasm of X. laevis oocytes. Second, the 100-kDa subunit of X. laevis CPSF forms a specific complex with RNAs that contain both a cytoplasmic polyadenylation element (CPE) and the polyadenylation element AAUAAA. Third, immunodepletion of the 100-kDa subunit of X. laevis CPSF reduces CPE-specific polyadenylation in vitro. Further support for a cytoplasmic form of CPSF comes from evidence that a putative homologue of the 30-kDa subunit of nuclear CPSF is also localized to the cytoplasm of X. laevis oocytes. Overexpression of influenza virus NS1 protein, which inhibits nuclear polyadenylation through an interaction with the 30-kDa subunit of nuclear CPSF, prevents cytoplasmic polyadenylation, suggesting that the cytoplasmic X. laevis form of the 30-kDa subunit of CPSF is involved in this reaction. Together, these results indicate that a distinct, cytoplasmic form of CPSF is an integral component of the cytoplasmic polyadenylation machinery.
在早期发育过程中，特定的信使核糖核酸（mRNA）在细胞质中接收多聚腺苷酸（poly(A)）。这种细胞质多聚腺苷酸化反应与翻译刺激相关，在某些情况下还会引发翻译刺激。此前有研究表明，一种类似于多亚基核切割和多聚腺苷酸化特异性因子（CPSF）的因子在细胞质多聚腺苷酸化中发挥作用。现在，编码非洲爪蟾（Xenopus laevis）CPSF 100 kDa亚基细胞质形式的互补脱氧核糖核酸（cDNA）已被分离出来。该蛋白质产物在氨基酸序列水平上与从牛胸腺中分离出的核CPSF有91%的同一性。本报告提供了三条证据，表明CPSF 100 kDa亚基的非洲爪蟾同源物参与了细胞质多聚腺苷酸化反应。首先，该蛋白质主要定位于非洲爪蟾卵母细胞的细胞质中。其次，非洲爪蟾CPSF的100 kDa亚基与同时含有细胞质多聚腺苷酸化元件（CPE）和多聚腺苷酸化元件AAUAAA的核糖核酸形成特定复合物。第三，去除非洲爪蟾CPSF的100 kDa亚基可降低体外CPE特异性多聚腺苷酸化。核CPSF 30 kDa亚基的推定同源物也定位于非洲爪蟾卵母细胞的细胞质中，这一证据进一步支持了CPSF的细胞质形式。通过与核CPSF的30 kDa亚基相互作用来抑制核多聚腺苷酸化的流感病毒NS1蛋白的过表达会阻止细胞质多聚腺苷酸化，这表明CPSF 30 kDa亚基的非洲爪蟾细胞质形式参与了这一反应。这些结果共同表明，一种独特的、细胞质形式的CPSF是细胞质多聚腺苷酸化机制的一个组成部分。
